Effects of ion beam surface modification on water absorption characteristics of perfluorosulfonic acid membranes

The dynamic behavior of water within ion beam (10 keV Ar ⁺, 1.0 × 10 ¹⁶-1.2 × 10 ¹⁷ ions/cm ²) modified perfluorosulfonic acid (PFSA) membranes was investigated at room temperature by combining direct-current (DC) resistance with alternative-current (AC) impedance methods under a water-saturated air atmosphere. The bulk impedance in existing surface sulfonate groups (SO ₃ ^-) decreased approximately one order of magnitude as a result of Ar ⁺ ion irradiation compared to the unirradiated membrane. The enhancement in the proton conductivity results in an improvement of the water absorption characteristics at the Ar ⁺ ion-modified surface which showed large superficies as well as hydrophilic radicals. These results can be explained in base of a relative increase in both the water content of the membrane and the change in the interactions of water molecules with sulfonate group at the interface on the proton-transfer process.